In differential pressure/pressure transmitting devices that are used for measuring flow rates, pressures, fluid levels, specific gravities, and the like, of process fluids in oil, petrochemical, and chemical plants, and the like, if the process fluid is a high-temperature, high-viscosity, corrosive, or coagulable fluid, a so-called remote sealed differential pressure/pressure transmitting device is used, wherein a pressure cell, for forming a pressure detecting portion, and a transmitting device main unit are connected together by a capillary tube that is filled with a filling fluid in order to transmit the pressure, where the pressure of the process fluid is received by a fluid-contacting diaphragm of the pressure cell and the dislocation of the fluid-contacting diaphragm is transmitted to the transmitting device main unit through the filling fluid. When a remote sealed differential pressure/pressure transmitting device is used, a flange is attached to the tank or pipe that will be subjected to measurement, and the pressure cell is interposed between this flange and an attachment flange, where the attachment flange is secured to the flange through a plurality of attachment bolts. See, for example, Japanese Unexamined Patent Application Publication H9-189634 (“JP '634”).
As illustrated in the JP '634, in a remote sealed differential pressure transmitting device that is made from such a structure, when the process fluid low-pressure side and high-pressure side pressures are applied to the fluid-contacting diaphragms of respective pressure cells, the fluid-contacting diaphragms dislocate and these dislocations are transmitted through the filling fluids to the transmitting device main unit, where the differential pressure at this time is converted into an electric signal by a semiconductor pressure sensor and subjected to calculation processing, making it possible to measure the flow rate of a process fluid. Note that while the explanation set forth above is for a differential pressure transmitting device, the exact same thing can be said for a pressure transmitting device as well. Consequently, in the present invention, the general term for both transmitting devices will be “differential pressure/pressure transmitting device.”
Japanese Unexamined Patent Application Publication 2002-156301 (“JP '301”) proposes an invention with a diaphragm structure wherein the diaphragm has a double-layer structure where diaphragms are layered together and electric circuits are formed on both diaphragms in order to detect quickly, through a detected electric current, a rupture of a diaphragm, because there have been cases wherein such fluid-contacting diaphragms have become corroded or swollen by the process fluid to then rupture.
Given this, this is a differential pressure/pressure transmitting device having a pressure transmitting portion able to transmit a pressure from a process through a diaphragm to a pressure transmitting fluid, and pressure detecting means for detecting pressure from the process by converting the pressure of the transmitting fluid into an electric signal, wherein the pressure transmitting portion is structured from process pressure detecting means wherein a process-side diaphragm that faces the process side and a fluid-contacting-side diaphragm that faces the pressure transmitting fluid are disposed facing each other in a state of contact, and wherein electrical contact points are provided at locations that face each other, and diaphragm rupture detecting means for detecting the state of contact of the electrical contact points of the process-side diaphragm and the fluid-contacting-side diaphragm.
Given this, in the invention of the JP '301, the two layers of diaphragms are layered together, and respective electrodes are provided in the centers thereof and caused to face each other. While normally the contact points thereof are in contact, if there is a rupture, or the like, then the contact points become separated, and the open circuit is detected, and thus the electrodes require delicate design and manufacturing in order to be mounted on the diaphragm, which is a thin plate.
However, the diaphragm is normally several dozen micrometers thick, making it difficult to provide an electrode, or the like, thereon. When an electrode is provided on the diaphragm, the stresses thereof will act on the diaphragm, having a negative effect on the actual pressure detecting characteristics of the diaphragm. On the other hand, if the electrodes are too thin, then there will be the risk of an electrode becoming broken through the operation of the diaphragm.
Given this, the problem in the present invention is to detect a rupture of a diaphragm without provision of electrodes on the diaphragms.